362 CARNEGIE INSTITUTION OF WASHINGTON. 



be expected, though in each case a skillful choice was made of the ma- 

 terials available. 



Biotic Succession in Bad Lands, hy F. E. Clements. 



The Bad Lands of the West have been actively studied since 1913. 

 More than sixty localities have been visited, many of them several 

 times. During the present summer, the Oligocene Bad Lands of Ne- 

 braska and South Dakota have been revisited, as well as the Permian 

 and Triassic Bad Lands of the Petrified Forest and the Painted Desert, 

 and the Cretaceous ones of southwestern Colorado and adjacent New 

 Mexico. The Wasatch exposures at Tatman Mountaiu were seen for 

 the first time, as were the Wmd River ones from Shoshoni eastward, 

 and the Lance from Gillette to Clearmont. The characteristic Red 

 Beds of the Spearfish and Chugwater formations were again studied 

 around the Black Hills and in central Wyoming. Finally, the Eocene 

 Bad Lands of the Puerco, Torrejon, and Wasatch formations of the 

 San Juan Basin in northern New Mexico were also visited for the first 

 time. 



Bad Lands are found in several climax associations of the West, 

 notably the mixed prairie, short-grass, bunch-grass, sagebrush, and 

 desert scrub. As areas of rapid erosion, they offer exceptional oppor- 

 tunities for the study of biotic succession at the present day, as evi- 

 denced by the succession of plant communities. These are deter- 

 mined by intensely xerophytic conditions as to soil, since the latter is 

 uniformly clay or a sandy clay. The climate is semiarid in the mixed 

 prairie and arid for all the other climaxes. The development of vege- 

 tation in the eroded valley plains produces stable conditions, each 

 marked by the climax, in which new erosion occurs. In the Oligocene 

 Bad Lands as many as five such erosion levels are found. The relative 

 age of these is readily determined by taking advantage of the fact 

 that the woody undershrubs of the valley plain stand above the sur- 

 face of the soil. The rate of erosion is found by dividing the height 

 of the short stem by the number of annual rings in it. 



The Bad Lands have been taken as the basis of an endeavor to or- 

 ganize the field of paleo-ecology in some detail. Since the deposits in 

 which they occur stretch from the Permian to the Pleistocene, they 

 afford an almost complete picture of the rise to dominance of the great 

 angiospermous flora and the great mammalian fauna. In addition, 

 the nature and structure of their deposits furnish abundant evidence 

 of the climate and topography at the time of deposition. These 

 bear a more or less dii'ect relation to conditions on the upland, and 

 through them it is hoped to obtain a more complete picture of upland 

 climate and vegetation, especially with respect to climatic cycles. In 

 this connection, measurements have been made of depositional layers 

 of all kinds in several formations, and it is hoped to extend this to many 



